Id move your plants into their own pots after they have 3 or 4 sets of true leaves... when they are that big you should pop one out of the container(I like that tray you have there btw). and if you see some white roots trying to pop through the jiffy pellet then you know its good to be transplanted. If not just stick it back in the tray for another week. I dont know much about LST but I have seen some really good results from growers who bend the plants down when they have about 6 nodes. Deciding when exactly to bend is up to you, If you do it early(5 or 6 nodes) it will be very easy to bend the stem. If you wait longer the stem will start to get stiff and it will take a bit more work to get it to horizontal without snapping it. If you wait longer you will also end up with more colas because there will be more nodes that will each become 2 colas. Earlier and you will get less colas but they will be more productive(per cola). So its up to you, you could easily let it grow to 4 feet before you start LSTing if you choose.